The invention relates to a method for actuating a pump having a reciprocating piston or a diaphragm for pressure generation in a hydraulic system, the reciprocating piston or the diaphragm being moved by way of an actuator which is driven by a magnetic field of a magnet coil, and a system pressure in the hydraulic system being determined.
Furthermore, the invention relates to a control device for actuating a pump having a reciprocating piston or a diaphragm for pressure generation in a hydraulic system, an actuator which is driven by a magnetic field of a magnet coil being provided for moving the reciprocating piston or the diaphragm, and a pressure sensor or an evaluation of a current flow through the magnet coil being provided to determine a system pressure in the hydraulic system.
In hydraulic systems without a return line, the pressure is usually generated by means of a reciprocating piston pump or a diaphragm pump. If required, a desired liquid quantity is removed via a metering device. A magnetically driven actuator for moving the piston or the diaphragm for the delivery stroke is provided in the pump. A spring is provided for the return of the piston or the diaphragm during a suction stroke. Setting of a desired setpoint pressure range can take place by means of a pilot control operation or in a closed control loop. Quantity control valves or pressure regulating valves or metering devices are typically used in order to realize the control loop. If the magnet coil which drives the magnetically driven actuator is actuated, the actuator performs a full stroke and the pump delivers a liquid quantity which is predefined by way of the magnitude of a delivery space. In order to return the actuator, either the actuating signal of the magnet coil is switched off and the magnetic field is dissipated via a freewheeling diode (“freewheel”) or an extinguishing diode or an ohmic resistance is additionally provided for an accelerated dissipation of the magnetic field (“rapid extinguishing”) across the magnet coil.
The switch-off by way of freewheeling has the advantage in comparison with the rapid extinguishing that the current through the magnet coil is dissipated more slowly and the electric loading and heat loss of the control unit are reduced. Since lower current gradients occur here, the electromagnetic compatibility (EMC) is more favorable. The noise emission of the pump is lower on account of the lower speed of the actuator during the return and the reduced speed during contact with the end position of the actuator. However, said slower suction stroke reduces the possible pump frequency and therefore the maximum possible delivery volume per unit time.
A higher pump frequency and therefore a higher quantity flow can be realized with a switch-off by way of rapid extinguishing. In this operating mode, however, the control unit is loaded by way of higher temperatures, and the noise emission of the pump is higher as a result of the higher contact speed of the actuator with the end stop.
Document DE 10 2008 042 987 A1 describes a metering apparatus for introducing liquids into an outlet space. The metering apparatus comprises a nozzle which opens into the outlet space and, furthermore, a metering unit having a metering valve. The metering valve comprises a valve stem which is guided in the valve body of the metering unit with the configuration of an intermediate space. The valve stem comprises at least one opening which makes the discharge of liquid into the intermediate space possible, the intermediate space being delimited by a flexible wall. Via the metering unit, the reducing agent can be injected into the outlet space via a pressure-controlled nozzle. Although DE 10 2008 042 987 A1 describes the technical environment, it does not disclose any regulating strategies as proposed by the present document.
DE 10 2012 009 729 A1 has disclosed a pressure delivery flow regulator for adjusting an adjusting unit of an adjustable hydraulic displacement machine, switching valves for actuating the adjusting unit being provided. According to claim 7, the switching valves of the adjusting unit can be actuated by way of an electronic control unit in a manner which is dependent on a pressure, in particular in a pressure line, and/or a displacement travel of the piston of the actuating cylinder. According to claim 8, the control unit can actuate the switching valves by way of a three-point control operation, in a manner which is dependent on the pressure. The three-point control operation is described in FIG. 2 and in paragraph [0044]. Here, the three-point control operation does not act by way of a single actuator which performs inward, outward and holding phases. Rather, the adjusting system overall, consisting of three actuators and the adjusting mechanism of the displacement machine, exhibits said behavior.